1. Field of the Invention
The present invention relates to a vehicle wheel driving apparatus arranging structure in which an axle of a road wheel and a rotational shaft of an in-wheel motor are disposed eccentrically with each other.
2. Description of Related Art
In recent years, on vehicles, techniques for disposing a motor inside a rim of a wheel have been under development in an attempt to simplify a power transmission apparatus from a power source to a wheel and enhance the power transmission efficiency. Since a vehicle wheel driving apparatus (in-wheel motor) like this is such as to drive a wheel which is a high load, an output torque is designed to be increased by reducing the rotational speed of the motor by a gear mechanism.
Consequently, vehicle wheel driving apparatus for practical use were not always such that an axle of a road wheel and a rotational shaft of a motor was caused to coincide with each other.
As a vehicle wheel driving apparatus arranging structure like this, there are known techniques in which an axle of a road wheel and a rotational shaft of a motor are disposed eccentrically with each other (refer to, for example, JP-A-2004-90822).
A technique disclosed in JP-A-2004-90822 will be described.
FIG. 6 is a diagram which describes a related basic configuration, and a vehicle wheel driving apparatus 200 is such that an upper arm 201, a lower arm 202 and a shock absorber 203 are caused to extend from a vehicle body side, an axle supporting member 204 is supported by the upper arm 201, the lower arm 202 and the shock absorber 203, a motor 205 is mounted on a supported side (housing side) of the axle supporting member 204, a rotational shaft of the motor 205 is connected to a shaft side of the axle supporting member 204, and a road wheel 208 made up of a wheel 206 and a tire 207 is mounted on the shaft side of the axle supporting member 204, and the motor 205 is disposed at the rear of the road wheel 208. In the figure, reference numeral 209 denotes an axle.
In the vehicle wheel driving apparatus 200 in which the axle 209 and the rotational shaft of the motor 205 are made eccentric with each other, however, the position of center of gravity of the road wheel 208 changes depending upon where the motor 205 is disposed in the wheel, whereby the magnitude of unsprung longitudinal oscillation of the road wheel 208 which is produced by an input from the road surface when the road wheel 208 runs over irregularities on the road surface or driving force from the motor. Consequently, when making the axle 209 and the rotational shaft of the motor 205 eccentric with each other, the motor 205 is desirably disposed in an optimum position of the wheel 206.
In addition, in the vehicle wheel driving apparatus 200, due to an increase in unsprung weight resulting from placing the motor in the wheel or realizing an in-wheel motor, the unsprung longitudinal oscillation of the road wheel 208, which is produced by an input from the road surface when the road wheel 208 runs over irregularities on the road surface or driving force from the motor 205, tends to be increased. Consequently, methods have been in need which can reduce effectively the unsprung longitudinal oscillation of the road wheel 208.
Namely, vehicle wheel driving apparatus arranging structures have been desired which allows a motor to be disposed in an optimum position in a wheel and which can reduce effectively the unsprung longitudinal oscillation of a road wheel.